This proposal is directed toward an understanding of the role of repetitive DNA sequences in gene expression. The slime mold Dictyostelium discoideum will be used as a test organism; the program will focus primarily on these points and in that order of priority: 1) Characterization of HnRNA-associated reiterated DNA transcripts isolated from amoebae at various stages of growth and development. Stage-specific sequences should be detected, if these transcripts serve a role in transcriptional control during cell differentiation. 2) Correlation of posttranscriptional modifications ('CAP' formation, poly A formation, chain cleavage, methylation) with specific classes of reiterated DNA transcripts associated with either HnRNAs or cytoplasmic mRNAs. 3) Reconstitution of an in vitro RNA processing system in a search for stage-specific maturation factors which may effect gene expression at the level of RNA processing. 4) Characterization of reiterated DNA transcripts in polysome-associated and in free cytoplasmic mRNAs isolated from different stages of development and growth. In the course of these studies an investigation of the occurrence of translational control of gene expression will be initiated.